The present invention relates to a laser cutting machine (hereinafter a recording apparatus), or more particularly, to an improvement to an apparatus for manufacturing an optical disk stamper (die assembly) useful in mass-producing an optical disk.
In recent years, several methods have been proposed for increasing the storage capacity of an optical disk. One of the methods is to physically raise the density of tracks, that is, to narrow a pitch between tracks. Another proposal has been made on the assumption that a finer pit is used for representing the same data, and standardization has progressed.
For narrowing a pitch between tracks, grooves defining each track or pits formed between the grooves must be made thinner. For this purpose, an optical system included in a recording apparatus employed during a mastering process or the like is controlled in order to make the diameter of a spot beam emanating from a laser smaller than that of a conventional spot beam.
A method utilizing super-resolution has been discussed. What is referred to as super-resolution is a phenomenon that a lens exhibiting a limit value of a numerical aperture (NA) that counts in cutting is used to make a spot laser beam, which has been diffraction-limited xcexNA, even smaller by utilizing the diffraction effects of light.
However, when the method utilizing super-resolution is adopted, the intensity of a first side lobe of a spot beam emanating from the laser increases. This adversely affects a disk during cutting. The adverse effect is intensified when cutting is carried out to form pits and grooves simultaneously.
For example, when cutting is carried out to form grooves consecutively, if a disk is exposed to a laser beam used to cut the disk for recording and it is modulated according to a certain signal (simultaneous cutting of pit and groove), the side lobe of the laser beam used for forming a pit overlaps a laser beam used for forming a groove. The power of the laser beam used for forming a groove increases substantially. As a result, a deep and broad groove is formed by the side of the pit. This poses a problem that an optical disk is manufactured from which signals properly representing pits and grooves respectively cannot be reproduced.
Accordingly, an object of the present invention is to provide a recording apparatus capable of manufacturing an optical disk from which signals properly representing pits and grooves respectively can be reproduced even when the density of tracks is physically increased.
A recording apparatus in accordance with the present invention for carrying out cutting so as to simultaneously form pits and grooves on the basis of a supplied pit signal and groove signal comprises: a pit cutting signal generating means for generating and outputting a pit cutting signal whose amplitude is proportional to each pit length or the length of each pit indicated by the pit signal; and a groove cutting signal generating means for generating a groove cutting signal by subtracting a magnitude of correction associated with each pit length indicated by the pit signal from the amplitude of the groove signal, and outputting the groove cutting signal according to the timing of outputting the pit cutting signal.
According to the constituent features, a magnitude of correction associated with each pit length indicated by the pit signal is subtracted from the amplitude of the groove signal in order to produce a groove recording signal. The groove recording signal is output according to the timing of outputting the pit cutting signal. Even when the side lobe of a laser beam used for forming pits overlaps a laser beam used for forming grooves, the power of the laser beam used for forming grooves is canceled by the power of the side lobe. Consequently, it will not take place that the depth or breadth of a portion of a groove adjacent to a pit gets larger than the other portions thereof.
According to a preferred embodiment of the present invention, when a pit length is relatively large, a magnitude of correction is set to a large value. When a pit length is relatively small, the magnitude of correction is set to a small value.
This is because when a pit length is relatively large, the possibility that a groove gets broader or deeper because of the aforesaid side lobe increases.